Many scenes, like Harry and Norman's conversation about making up the ULF report and dealing with Ted, were completely improvised.

[?] Joseph Hahn, the DJ in rock band [?] Linkin Park, designed the sea snake.

The ending had to be reshot because test audiences could not believe that the characters could survive without spending weeks in decompression.

When Harry suggests that Ted try to translate the communication using binary, the subsequent display is in base-10, not binary.

The jellyfish attack sequence used a combination of puppets, computer-generated images, and footage of real jellyfish filmed at a nearby aquarium. The footage of real jellyfish was played at three to five times its normal speed to make the jellyfish appear more aggressive.

The scene where Harry (Samuel L. Jackson) nearly chokes when he hears he is eating fried squid was not in the original novel, and was most likely added as a reference to the infamous 'chestburst scene' from Alien.